Mesoporous potassium-intercalated layered titanate has been synthesized through a reassembling of exfoliated titanate nanosheets and potassium cations. According to powder X-ray diffraction, electron microscopy, and N2 adsorption–desorption isotherm analyses, the intercalation of potassium ions gave rise not only to a slight basal expansion of the layered titanate but also to the formation of mesoporous assembly of the layered crystallites. In comparison with the pristine cesium titanate and its protonated derivative, the mesoporous potassium-intercalated titanate showed better photocatalytic activity for the photodegradation of organic molecules and higher adsorption capability for organic dye and CO2 molecules, as well.